The inventor of the embodiments herein is the inventor of a number of methods and apparatuses for forming light emitting diode circuits without wire bonding or solder. Some of the prior US patents of the inventor disclosing related prior inventions include, among others in the US and internationally, U.S. Pat. Nos. 7,952,107, 7,858,994, 7,259,030, 7,294,961, 7,723,733, the disclosures of which are incorporated by reference herein.
The present invention pertains to method of forming a bare die LED light sheet. The inventive methods and apparatuses can be used to make a photo-radiation source for applications including, but not limited to, general illumination, architectural lighting, novelty lighting, display backlighting, heads-up displays, commercial and roadway signage, monochromatic and full-color static and video displays, a radiation-source for photo-curable materials, patterned light emissive images, scrolling displays, friend or foe identification, light sources for the transportation industry including trucks, cars, boats, airplanes, and the like. Further, the present invention can be used to make enhanced electronically active sheets utilizing bare die electronic semiconductor elements such as transistors, resistors, capacitors, etc.
Inorganic light emitting diodes (LED) are based on elements of the periodic table of a vast variety. They come out of semiconductor technology, and indeed, a semiconductor diode such as a silicon diode, or a germanium diode were among the first semiconductor devices. These were made by doping the silicon or the germanium with a small amount of impurity to make n-type (excess electrons) or p-type (excess holes) in the material. LEDs emit light because of the materials selected so that the light is emitted in the ultra-violet, visible, or infrared ranges of the spectrum. The types of materials used are made from vapor deposition of materials on semiconductor wafers and cut into dice (a single one is a die). Typically, the die, or LED dice, are about 12 mil sq. The composition of the dice depends on the color, for example some red dice are AlInGaAs and some blue dice are InGaN. The variations are typically “three-five” variations, so-called because the n- and p-type materials forming the diode are based on the third and fifth period of the periodic table.
The conversion of an LED die into an LED lamp is a costly process, involving very precise handling and placement of the tiny LED die. The LED dice are most simply prepared as 3 mm LED lamps. The die is robotically placed in a split cup with wire leads on each side. A bottom conductor of the die is fixed in electrical communication with the cup using, for example, a conductive adhesive or solder, with one wire lead integrally formed with the cup. The other wire lead is connected to a top conductor of die by wire bonding, where a thin wire is used to connect that top conductor to the other wire lead. The entire structure is 2 encased in a plastic lens that attempts to focus the beam more narrowly. High brightness dice may also be surface mounted with current-driving and voltage limiting circuits, and elaborate heat sink and heat removal schemes. The LED lamp has the pair of leads, which can then be soldered to a printed circuit board. Although the cost of the bare die can be fairly cost effective, the cost of forming the lamp and then soldering the lamp to a printed circuit board is a relatively expensive process.
The demand for more efficient solid-state lighting continues to grow. There is a growing desire to reduce the dollar and environmental costs associated with the formation of a conventional LED packaged lamp or chip-on-board array used by these solid-state light bulbs. Accordingly, there is a need to reduce the cost of forming a light emitting device based on the LED die.
A common failure mechanism for electronic circuits occurs due to thermal cycling caused by heat generated during the operation of the circuit. Conventionally, heat sinks are used to draw heat away from the electronic circuits and transfer the heat as efficiently and quickly as practical to the ambient. A fan is often used to facilitate removing heat from the heat sink.
As an example of a recent prior attempt providing a commercially available LED lighting solution in the transportation industry, Grote Industries of Madison, Ind., has introduced LED designs that combine dual functions using long life LED technology, to create an obvious but useful step forward where stop/signal/tail and back-up lighting functions are combined in a single unit. Grote claims that replacing conventional incandescent lamps with modern LEDs results in a lamp that can last the life of the vehicle it's installed on. However, even this recent attempt to provide an LED lighting solution for the transportation industry fails to provide effective shock proofing, thermal management and water proofing to consistently and effectively withstand many of the environmental, ambient and service conditions that a lighting device experiences, for example, when used as a stop/signal/tail and back-up on a highway bound tractor tailer. Failure of any of these critical functional features of the conventional lighting device can result in a catastrophic accident, leading to considerable losses in terms of material goods, vehicles, personal injuries and even death.
Accordingly, there is a need to provide an improvement to the LED lighting solutions that are commercially available for industries, such as the transportation industry.